Elemental concentrations in different compartments of rapidly frozen chromaffin cells have been measured with the aim of elucidating ionic changes that occur during secretion. Some cells were prepared under resting conditions as controls while other cells were stimulated with nicotine or potassium. In addition, intragranular pH was increased by treatment with NH4Cl to inhibit secretion. Cells were rapidly frozen against a liquid helium cooled copper block and ultrathin frozen cryosections were prepared. Sections were freeze-dried in an analytical electron microscope and energy-dispersive x-ray spectra were obtained from granules, nuclei, cytoplasm and mitochondria. Concentrations of Na, Mg, P, S, Cl, K and Ca were obtained using ML spectral fitting.